Quantified Volatility Distributions from Monoterpene SOA

DAVID BELL, Jun Zhang, Jens Top, Natasha Garner, Fabian Mahrt, Mihnea Surdu, André S. H. Prévôt, Imad El Haddad, Paul Scherrer Institute

     Abstract Number: 351
     Working Group: Aerosol Chemistry

Abstract
The saturation vapour concentration (Log C*) of a molecule represents a key variable that governs the ability of molecules to nucleate new particles and partition into pre-existing aerosols. Thus, the saturation vapour concentration affects the chemical composition and the mass yields of ambient aerosol, ultimately affecting air pollution and climate. The determination of saturation vapour concentration is straightforward for small molecules, and those readily synthesized. In the atmosphere, the oxidation of volatile organic compounds creates a complex mixture of organic molecules in both the gas and condensed phase. Such mixtures or their individual molecules cannot be readily obtained as commercial standards, to determine their saturation vapour concentrations.

A thermal denuder coupled to a scanning mobility particle sizer (TD-SMPS) has been employed to determine the saturation vapour concentration of single component systems. However, the lack of chemical resolution prevents its applicability to determine the saturation vapour concentration of more complex organic mixtures such as secondary organic aerosol (SOA). Consequently, considerable uncertainties still exist regarding the saturation vapour concentration of ambient SOA components and hence the impact of SOA for air pollution and climate. To address this, we deployed an extractive electrospray ionization mass spectrometer (EESI-MS) coupled with a TD-SMPS (hence TD-SMPS+EESI) to provide molecular formula separation of complex mixtures together with their saturation vapour concentrations. We performed measurements on a complex mixture of known species (PEG-300) and then utilized SOA types derived from the ozonolysis of monoterpenes in an atmospheric simulation chamber.

Coupling this method with quantified measurements of grouped monomers, dimers, and higher order oligomers, we can provide a quantified volatility distribution for SOA derived from different monoterpenes. We will discuss the systematic differences in the volatility distribution of SOA from monoterpenes, as well as how they evolve during chamber experiments.